Polyurethane foam laminates

ABSTRACT

A structure is disclosed comprising a layer of polyurethane foam bonded to at least one layer of another material, especially a layer of fibreglass matte, a layer of cellulosic material e.g. cardboard, and/or a layer of polyurethane foam. The layers are bonded together with an adhesive of polyethylene or polypropylene that has been grafted with an ethylenically unsaturated dicarboxylic acid or anhydride thereof, the adhesive containing at least 0.03% by weight of said acid or anhydride. The structure exhibits a temperature for heat-fail resistance in shear of at least 90° C. In embodiments, the polyurethane foam is a rigid polyurethane foam, and the polyethylene and polypropylene have been grafted with fumaric acid, maleic acid or maleic anhydride. As an example, the structure is comprised of a layer of fibreglass matte, at least one layer of polyurethane foam and a layer of fibreglass matte, the layers being bonded together with the adhesive. The structure may be used as so-called headliners in automobiles.

The present invention relates to laminates of polyurethane foam andespecially to laminates of polyurethane foam with fibreglass matte,cellulasic structures e.g. cardboard, and/or polyurethane foam. Inparticular, the invention relates to such laminates having a temperaturefor heat-fail resistance in shear, a measurement of the temperature atwhich delamination of a laminate occurs, of at least 70° C.

Laminates of polyurethane foams with fibreglass matte and/or cardboardare used in a number of end-uses, particularly in the form of liners forpassenger compartments of automobiles i.e. as so-called headliners. Suchliners are often multi-layered structures, usually having an outer layerof a fabric material for aesthetic reasons. The traditional adhesive forsuch structures is a polyurethane adhesive, which has given liners ofacceptable structural properties. However, polyurethane adhesives areincreasingly in disfavour because of environmental and occupationalhealth objections to the use of isocyanate-containing adhesives. Thus,alternate adhesives are required that do comply with environmental andoccupational health requirements, as well as meet product specificationsfor the resultant bonded structure. Moreover, any such adhesive shouldbe economical.

As used herein, a "rigid foam" is defined according to thespecifications in ASTM D1566-82 entitled "Definitions of Terms Relatingto Rubber".

As used herein, "temperature for heat-fail resistance in shear" ismeasured according to the procedure of ASTM D4498 entitled Heat-FailTemperature in Shear of Hot-Melt Adhesives, except that the weight usedwas 300 g; use of heavier weights may result in physical failure of thepolyurethane foam layer.

It has now been found that polyethylene and polypropylene grafted withan ethylenically unsaturated dicarboxylic acid or anhydride, optionallyin the form of grafted polymer blended with ungrafted polymer, may beused in the bonding of polyurethane foam structures, without the use ofisocyanates.

Accordingly, the present invention provides a structure comprising:

a layer of polyurethane foam bonded to at least one of a layer offibreglass matte, a layer of cellulosic material and a layer ofpolyurethane foam; said layers being bonded together with an adhesive ofpolyethylene or polypropylene that has been grafted with anethylenically unsaturated dicarboxylic acid or anhydride thereof, orderivative thereof, said adhesive containing at least about 0.03% byweight of said acid or anhydride; and

said structure exhibiting a temperature for heat-fail resistance inshear of at least 70° C., preferably at least 90° C.

In a preferred embodiment of the structure, the polyurethane foam is arigid polyurethane foam.

In a further embodiment, the polyethylene and polypropylene have beengrafted with at least one of fumaric acid, maleic acid, maleicanhydride, maleimide, nadic anhydride and acrylic acid, or derivativesthereof.

In another embodiment, the structure is comprised of a layer offibreglass matte, at least one layer of polyurethane foam and a layer offibreglass matte, the layers being bonded together with said adhesive.

The present invention provides a structure comprising:

a layer of polyurethane foam bonded to at least one of a layer ofanother material;

said layers being bonded together with an adhesive of polyethylene orpolypropylene that has been grafted with an ethylenically unsaturateddicarboxylic acid or anhydride thereof, or derivative thereof, saidadhesive containing at least about 0.03% by weight of said acid oranhydride; and

said structure exhibiting a temperature for heat-fail resistance inshear of at least 70° C., preferably at least about 90° C.

The present invention relates to structures of polyurethane foamlaminated to other materials, and will be particularly described withreference to laminates to fibreglass matte, cellulosic material and/orpolyurethane foam, especially with respect to use of fibreglass matte.The cellulosic material is particularly in the form of a cardboard butother forms of cellulosic material, especially relatively flexiblecellulosic material may be used. The surface of the cellulosic materialmay be treated, provided that any such treatment does not significantlyadversely affect the bonding mechanism e.g. polyethylene-coatedcardboard may be used. The fibreglass is in the form of a layer offibreglass matte. It would normally be flexible to the extent that thelayer is capable of being bent or shaped to conform to a curved surfacee.g. the shape of a headliner in an automobile. The fibreglass may betreated with a finish e.g. a size or primer, as long as the finish doesnot significantly adversely affect the bonding mechanism. The thicknessof the fibreglass matte may be varied over a wide range, although it ispreferred that the matte be relatively thin, to prevent or reduce thelikelihood of delamination of the matte. In one embodiment, thethickness is about 0.05 cm and the fibreglass matte is a non-woven matteformed from glass fibres having a length of about 5 cm.

The polyurethane foam may be and preferably is a rigid foam, although itmay also be a flexible foam. If the foam is a rigid foam, it preferablypossesses a small degree of flexibility, so that it is capable of beingconformed to the shape of a curved surface, although an inflexible rigidfoam could be formed into the required shape using a thermoforming orother process. The thickness of the polyurethane foam may be varied overa wide range, although in one embodiment it is preferred that the foambe relatively thin for convenience and for versatility in themanufacturing process. As an example, in one embodiment the thickness isabout 0.5 cm. The pore size of the foam may be varied over a wide range,a preferred range being 0.1-1.0 mm.

The adhesive is a grafted polyethylene or grafted polypropylene. Thepolymer may be grafted polymer per se or in the form of an un-graftedpolymer blended with a grafted polymer. The polymer may be a homopolymerof ethylene or a copolymer of ethylene with a minor amount e.g. up to20% by weight, of at least one higher hydrocarbon alpha-olefin having3-20, especially 3-10 and particularly 4-10, carbon atoms. Examples ofthe higher hydrocarbon alpha-olefins include propylene, butene-1,4-methyl pentene-1, hexene-1 and octene-1, and mixtures thereof, ormixtures of two or more of the higher hydrocarbon alpha-olefins. Suchpolymers may have a density of from about 0.850 g/cm³ up to about 0.965g/cm³, especially 0.890 g/cm³ up to about 0.965 g/cm³ i.e. the polymersinclude so-called high density polyethylene, low density polyethyleneand very low density polyethylene, especially polyethylene having adensity of at least 0.940 g/cm³. However, the temperature of bondingpermissible or achievable in the process of manufacture of thestructures may dictate that a polyethylene of lower density, or lowermelting point, be used. In addition, the polymers have a melt index, asmeasured by the procedure of ASTM D1238 (Condition E), in the range offrom about 0.1 dg/min to about 200 dg/min, especially 1-80 dg/min and inparticular in the range 2-70 dg/min. Alternatively, the polymer may be apolypropylene, especially a homopolymer of propylene or a copolymer ofpropylene and a minor amount of ethylene. Such polymers are known andare available commercially.

The polymer is grafted with an ethylenically unsaturated dicarboxylicacid or anhydride, or derivatives thereof. Preferred examples of such anacid or anhydride are fumaric acid, maleic acid, maleic anhydride,maleimide, nadic anhydride, acrylic acid, citraconic acid, citraconicanhydride, itaconic acid, itaconic anhydride,endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid,endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid anhydride,cis-4-cyclohexene 1,2 dicarboxylic acid, cis-4-cyclohexene 1,2dicarboxylic acid anhydride, and derivatives thereof. Metal salts,anhydrides, esters, amides or imides of the above acids may also beuseful. Ordinary skill and experimentation may be necessary in selectingany particular grafting monomer, depending on the performancerequirements of the particular application. Maleic acid and maleicanhydride are especially preferred. The grafted polymer should containat least about 0.03%, by weight, of the grafted monomer. In preferredembodiments, the grafted polymer contains at least 0.07% and especiallyat least 0.10% by weight of grafted monomer. Examples of such graftedpolymers are available commercially, for instance from Du Pont CanadaInc. under the trade mark Fusabond or may be manufactured by processesknown in the art. An example of the latter is the process described inU.S. Pat. No. 4,612,155 of C. S. Wong and R. A. Zelonka, which issued1986 Sep. 16.

The adhesive may contain additives provided that such additives do notdetract from the performance of the adhesive. A variety of materials arecommonly used and known in the adhesive art, such as, for example,antioxidants, surface modifiers, stabilizers, fillers, extenders, waxes,foaming agents, pigments, anti-static agents, and crosslinking agents.

Antioxidants generally protect the stability of the adhesive whensubjected to heat, or during long term storage in bulk form. Suitableantioxidants include typical hindered phenols such as for example,butylated hydroxytolunes (BHT), ETHYL® 330 and IRGANOX® 1010, believedto be neopentanetetrayl 3,5-di-tert-butyl-4-hydroxy cinnamate, as wellas phosphites.

Surface modifiers, such as for example, amide slip agents, such asstearamide, and silica can be used to advantage in adhesive compositionsof this invention.

Certain additives customarily employed in adhesive formulations mayinterfere with the bonding ability of compositions of this invention.The practioner of ordinary skill will be able to determine the negativeeffect of a potential additive with minimum experimentation.

The structure of the invention is in the form of a laminate of a layerof polyurethane foam bonded or laminated to a layer of fibreglass matteand/or a layer of polyurethane foam. That structure is bonded togetherby the adhesive described above. In embodiments, the structure is amulti-layered structure. For instance, the structure could be comprisedof layers of, in sequence, fibreglass matte, polyurethane foam andfibreglass matte, or a layer of fibreglass matte, multiple layers ofpolyurethane foam and another layer of fibreglass matte. For example,the structures could be: ##STR1## In the preferred end-use, theindividual layers are relatively thin e.g. in the range of 0.2-1.0 cmfor the polyurethane foam and in the range of 0.02-0.1 cm for fibreglassmatte. However, the thickness of the layers is primarily determined bythe intended end-use.

The structure may be manufactured by laminating the layers in a pressunder heat and pressure. For instance, the various layers may be formedinto a sandwich of the required construction and then inserted into thepress. The temperature and period of time in the press will depend on,for example, the particular construction and thickness thereof as wellas the particular grafted polyethylene or polypropylene selected for theadhesive layer. Examples of temperatures and pressures are given in theexamples below. Alternatively, the adhesive may be applied in powderform, as a non-woven sheet or by using a porous coat system e.g. acoating system that applies a fibre or web e.g. a number of randomstrands, of adhesive onto a substrate and essentially forms a non-wovenadhesive layer. The adhesive could also be the outer layer of amulti-layer laminate.

In one embodiment of processes for the manufacture of headliners, steamis injected into the mould during the bonding process at a temperaturesufficient to melt the adhesive, with the entire headliner panel beingunder pressure; open-celled foams permit the escape of any steam usedduring the bonding process. The foam may be formed by the reaction of apolyisocyanate with a polyol using a foaming agent that is a gaseoushydrocarbon or fluorocarbon, or other inert gas, e.g. nitrogen.Thermoforming-type bonding processes e.g. with the adhesive pre-appliedto one of the layers or components of the laminate or insertedseparately into the process, may also be used.

The laminated structure is preferably sufficiently flexible so as to bemoulded to the shape of a mould, although as noted above it is possibleto use inflexible layers e.g. inflexible polyurethane layers, may beused. Such a mould would normally be a curved mould e.g. as in aheadliner for an automobile, with relatively few sharp angles. In such ause, the structure would normally be bonded to at least one additionallayer e.g. a layer of fabric material which would be the visible layere.g. the layer visible inside the automobile. The structure may also bebonded to other materials e.g. aluminum foil, other metals and otherpolyolefins for automotive or other end-uses. Examples of the latterinclude thermal insulation materials for the construction industry,insulation for refrigerated truck trailers, bodies and railcars, andinsulation for oil tanks, and the like.

The structures of the invention have a temperature of heat-failresistance in shear of at least 70° C. and preferably at least 90° C.Such temperatures are important in the automotive industry, for example,because headliners tend to get hot when the automobile is sitting in thesun and acceptable temperature preformance is required.

Although the present invention has been described herein with particularreference to the bonding of glass matte to rigid polyurethane foam, theinvention may also be used in the bonding of rigid polyurethane foam torigid polyurethane foam, glass matte to flexible polyurethane foam, andother combinations of rigid polyurethane foam, flexible polyurethanefoam and glass matte, bonding to cellulosic materials, and including thebonding of like and of dissimilar materials.

The present invention is illustrated by the following examples.

EXAMPLE I

A laminate of fibreglass matte and a polyurethane foam was formed, withthe layers being bonded together using a film of adhesive. Thefibreglass was a non-woven matte having a thickness of approximately 0.5mm that had been formed from glass fibres having a length of about 5 cm.The polyurethane foam was a polyether polyurethane identified by thetrade mark "Foamex", with a density of about 0.025 g/cm³, a thickness of0.5 cm and pore sizes that were predominantly in the range of 0.25-0.5mm. The adhesive film was in sheet form, with a thickness of 0.18 mm.

The adhesive was formed from a polymer, and optionally contained agrafted polymer; the grafted polymer, when used, was used as a blendwith the indicated polymer in an amount of 10% by weight. The polymerwas a polyethylene, the polymers with densities of about 0.96 beinghomopolymers of ethylene and the polymers with lower densities beingcopolymers of ethylene and butene-1. The grafted polymer was a highdensity linear ethylene homopolymer having a density of 0.96 g/cm³, amelt index in the range of 2.0 dg/min and which had been grafted with 1%by weight of maleic anhydride.

The structure was laminated by heating in a press at a temperature of140° C. for 30 seconds under a pressure of 103 kPa.

The laminate obtained was tested using the procedure of ASTM D4498,except that because of the lack of strength of the polyurethane foamunder test conditions, the weight used was 300 g. One part of thelaminate was clamped and the other part, with weight attached, wasallowed to hang freely. The sample was located in a temperaturecontrolled oven. The test involved increasing the temperature of theoven until the adhesive bond failed.

Further details and the results obtained are given in Table I.

                  TABLE I                                                         ______________________________________                                                                   Contains                                           Run     Polymer  Melt      Grafted                                                                              Fail Temp.                                  No.     Density  Index     Polymer                                                                              (°C.)                                ______________________________________                                        1       0.895    12        no     82.0                                        2       0.930    73        no     99.4                                        3       0.959    65        no     86.7                                        4       0.895    12        yes    120                                         5       0.930    73        yes    110                                         6       0.959    65        yes    >120                                        ______________________________________                                    

The results show that the presence of maleic-anhydride graftedpolyolefin greatly improves the temperature performance, as compared tothe un-grafted polyolefin composition.

EXAMPLE II

The procedure of Example I was repeated, bonding a rigid polyurethanefoam to rigid polyurethane foam using the maleic-anhydride graftedpolyethylenes of Example I. The results obtained are given in Table II.

                  TABLE II                                                        ______________________________________                                                                   Contains                                           Run     Polymer  Melt      Grafted                                                                              Fail Temp.                                  No.     Density  Index     Polymer                                                                              (°C.)                                ______________________________________                                        7       0.895    12        yes    129.0                                       8       0.930    73        yes    130.7                                       9       0.959    65        yes    137.7                                       ______________________________________                                    

The results show that the grafted polyolefin adhesive blend providedoutstanding heat resistance.

EXAMPLE III

A laminate of fibreglass matte and polyurethane foam was formed, withthe layers being bonded together using a film of adhesive, following theprocedure of Example I.

The laminates were subjected to a creep test, using samples as preparedin Example I for the shear adhesion fail test of ASTM D4498. The testsample was placed in a temperature-controlled oven using a 100 g weight;one part of the laminate was clamped and the other part, with weightattached, was allowed to hang freely. The samples were kept at acontrolled temperature for one month, after which the temperature wasraised by 10° C. and the procedure repeated. The temperature at whichthe adhesive bond failed was recorded.

Further details and the results obtained are given in Table III.

                  TABLE III                                                       ______________________________________                                                             Creep Failure                                                                             SAFT*                                        Run No.  Adhesive    Temp (°C.)                                                                         (°C.)                                 ______________________________________                                        10       A           140         138                                          11       B           140         137                                          12       C           >150        149                                          13       D           >150        130                                          14       E           140         119                                          15       F           110          91                                          16       G           110          88                                          ______________________________________                                         *SAFT = Heat Fail Temperature in Shear                                        Adhesive A = 85.65% ungrafted high density polyethylene; 14% grafted high     density polyethylene (0.9585 g/cm.sup.3, melt index of 3 dg/min, 1.0% by      weight of maleic anhydride); 0.35% neopentanetetrayl                          3,5di-tert-butyl-4-hydroxy cinnamate antioxidant, final composition havin     a melt index of 4.3 dg/min and 0.14% by weight of maleic anhydride            Adhesive B = 83.2% ungrafted high density polyethylene; 16.7% grafted hig     density polyethylene (0.9585 g/cm.sup.3, melt index of 3 dg/min, 1.0% by      weight of maleic anhydride); 0.1% neopentanetetrayl                           3,5di-tert-butyl-4-hydroxy cinnamate antioxidant, final composition havin     a melt index of 4.7 dg/min and 0.17% by weight of maleic anhydride)           Adhesive C = 77% by weight of polypropylene; 20% by weight of linear low      density polyethylene and 3% by weight of grafted polypropylene, the final     composition having a melt index of 3.6 dg/min and containing 0.10% by         weight of maleic anhydride                                                    Adhesive D = 90% high density polyethylene (0.959 g/cm.sup.3, and melt        index of 65 dg/min; 10% grafted high density polyethylene (0.9583             g/cm.sup.3, melt index of 3 dg/min and containing 1.0% by weight of malei     anhydride                                                                     Adhesive E = 80% high density polyethylene (0.959 g/cm.sup.3, melt index      of 65 dg/min); 20% grafted high density polyethylene (0.9585 g/cm.sup.3,      melt index of 3 dg/min and containing 1.0% by weight of maleic anhydride)     Adhesive F = zinc ionomer, melt index of 5.2 dg/min                           Adhesive G = zinc ionomer, melt index of 0.7 dg/min                      

The samples of the adhesives of the invention gave substantially bettercreep results than the samples based on ionomers. The grafted adhesivesgave better shear adhesion fail temperatures than the related ungraftedadhesives.

I claim:
 1. A structure comprising:a layer of polyurethane foam bondedto at least one of a layer of another material; said layers being bondedtogether with an adhesive of polyethylene or polypropylene that has beengrafted with an ethylenically unsaturated dicarboxylic acid or anhydridethereof, or derivative thereof, said adhesive containing at least about0.03% by weight of said acid or anhydride; and said structure exhibitinga temperature for heat-fail resistance in shear of at least 70° C. 2.The structure of claim 1 in which the temperature for heat-failresistance in shear is at least 90° C.
 3. A structure comprising:a layerof polyurethane foam bonded to at least one of a layer of fibreglassmatte, a layer of cellulosic material and a layer of polyurethane foam;said layers being bonded together with an adhesive of polyethylene orpolypropylene that has been grafted with an ethylenically unsaturateddicarboxylic acid or anhydride thereof, or derivative thereof, saidadhesive containing at least about 0.03% by weight of said acid oranhydride; and said structure exhibiting a temperature for heat-failresistance in shear of at least 70° C.
 4. The structure of claim 3 inwhich the temperature for heat-fail resistance in shear is at least 90°C.
 5. The structure of claim 1 in which the polyurethane foam is a rigidpolyurethane foam.
 6. The structure of claim 1 in which the polyethyleneand polypropylene have been grafted with at least one of fumaric acid,maleic acid, maleic anhydride, maleimide, nadic anhydride, acrylic acid,citraconic acid, citraconic anhydride, itaconic acid, itaconicanhydride, endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid,endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid anhydride,cis-4-cyclohexene-1,2 dicarboxylic acid, cis-4-cyclohexene 1,2dicarboxylic acid anhydride, and derivatives thereof.
 7. The structureof claim 2 in which the polyethylene and polypropylene have been graftedwith at least one of fumaric acid, maleic acid, maleic anhydride,maleimide, nadic anhydride, acrylic acid, citraconic acid, citraconicanhydride, itaconic acid, itaconic anhydride,endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid,endo-bicyclo-[2.2.1]-5-heptene-2,3 dicarboxylic acid anhydride,cis-4-cyclohexene 1,2 dicarboxylic acid, cis-4-cyclohexene 1,2dicarboxylic acid anhydride, and derivatives thereof.
 8. The structureof claim 1 in which the structure is comprised of layers of glass matteand polyurethane foam.
 9. The structure of claim 1 in which thestructure is comprised of a layer of fibreglass matte, at least onelayer of polyurethane foam and a layer of fibreglass matte, the layersbeing bonded together with said adhesive.
 10. The structure of claim 1in which the adhesive is grafted polyethylene.
 11. The structure ofclaim 1 in which the adhesive is grafted polypropylene.
 12. Thestructure of claim 10 in which the polyethylene is high densitypolyethylene.
 13. The structure of claim 10 in which the polyethylene islow density or very low density polyethylene.
 14. The structure of claim1 in which the adhesive contains at least 0.7% by weight of grafted acidor anhydride.
 15. The structure of claim 1 in which the layers ofpolyurethane foam have a thickness of 0.2-1.0 cm and the fibreglassmatte has a thickness of 0.02-0.1 cm.
 16. The structure of claim 1 inwhich each layer has sufficient flexibility to be able to be bent orshaped to conform to a curved surface.
 17. The structure of claim 1 inwhich the adhesive is formed form a blend of grafted and ungraftedpolyethylene or polypropylene.